CN113748675A

CN113748675A - Video coding and decoding method and apparatus using improved matrix-based intra prediction coding and decoding mode

Info

Publication number: CN113748675A
Application number: CN202080028123.XA
Authority: CN
Inventors: 马宗全; 王祥林; 陈漪纹; 修晓宇; 朱弘正; 叶水明; 郑云飞
Original assignee: Beijing Dajia Internet Information Technology Co Ltd
Current assignee: Beijing Dajia Internet Information Technology Co Ltd
Priority date: 2019-04-10
Filing date: 2020-04-09
Publication date: 2021-12-03
Also published as: CN114501000A; WO2020210489A1; EP3939269A1; EP3939269A4; US20240314303A1; CN118488193A; CN118488194A; CN114501000B; US20220030228A1

Abstract

The electronic device performs a method of updating a most probable mode candidate list for a current block of video data. The electronic device first identifies neighboring blocks located at predefined positions relative to the current block and their associated matrix-based intra prediction modes. Next, the electronic device determines a conventional intra-prediction mode corresponding to the matrix-based intra-prediction mode for the neighboring block according to a predefined mathematical relationship between the conventional intra-prediction mode and the matrix-based intra-prediction mode. Finally, the electronic device inserts conventional intra-prediction modes associated with the neighboring blocks into a most probable mode candidate list according to a predefined order. If the conventional intra prediction mode is signaled in the semantics of the video bitstream that includes the current block, the video decoder will predict the current block from the reconstructed neighboring blocks according to the conventional intra prediction mode.

Description

Video coding and decoding method and apparatus using improved matrix-based intra prediction coding and decoding mode

Technical Field

The present application relates generally to video data encoding and decoding and, in particular, to methods and systems for video coding using a matrix-based intra prediction (MBIP) coding mode.

Background

Various electronic devices, such as digital televisions, laptop or desktop computers, tablet computers, digital cameras, digital recording devices, digital media players, video game consoles, smart phones, video teleconferencing devices, video streaming devices, and the like, support digital video. Electronic devices transmit, receive, encode, decode, and/or store digital video data by implementing video compression/decompression standards as defined by the MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced Video Codec (AVC), High Efficiency Video Codec (HEVC), and general video codec (VVC) standards. Video compression typically includes performing spatial (intra) prediction and/or temporal (inter) prediction to reduce or remove redundancy inherent in the video data. For block-based video coding, a video frame is partitioned into one or more slices, each slice having a plurality of video blocks, which may also be referred to as Coding Tree Units (CTUs). Each CTU may contain one Codec Unit (CU), or be recursively divided into smaller CUs until a predefined minimum CU size is reached. Each CU (also referred to as a leaf CU) contains one or more Transform Units (TUs), and each CU also contains one or more Prediction Units (PUs). Each CU may be coded in intra mode, inter mode, or IBC mode. Video blocks in an intra-coded (I) slice of a video frame are encoded using spatial prediction with respect to reference samples in neighboring blocks within the same video frame. Video blocks in an inter-coded (P or B) slice of a video frame may use spatial prediction with respect to reference samples in neighboring blocks within the same video frame, or temporal prediction with respect to reference samples in other previous and/or future reference video frames.

A prediction block for a current video block to be coded is derived based on spatial prediction or temporal prediction of a reference block (e.g., a neighboring block) that has been previously coded. The process of finding the reference block may be accomplished by a block matching algorithm. Residual data representing pixel differences between the current block to be coded and the prediction block is called a residual block or prediction error. The inter-coded block is coded according to a motion vector and a residual block, the motion vector pointing to a reference block forming a prediction block in a reference frame. The process of determining motion vectors is commonly referred to as motion estimation. The intra coded block is coded according to an intra prediction mode and a residual block. For further compression, the residual block is transformed from the pixel domain to a transform domain (e.g., frequency domain), resulting in residual transform coefficients, which may then be quantized. The quantized transform coefficients, initially arranged in a two-dimensional array, may be scanned to produce one-dimensional vectors of transform coefficients, and then entropy encoded into a video bitstream to achieve even greater compression.

The encoded video bitstream is then stored in a computer readable storage medium (e.g., flash memory) for access by another electronic device having digital video capabilities or directly transmitted to the electronic device, either wired or wirelessly. The electronic device then performs video decompression (which is the reverse of the video compression described above), e.g., by parsing the encoded video bitstream to obtain semantic elements from the bitstream and reconstructing the digital video data from the encoded video bitstream to its original format based at least in part on the semantic elements obtained from the bitstream, and the electronic device presents the reconstructed digital video data on a display of the electronic device.

As the digital video quality changes from high definition to 4K × 2K or even 8K × 4K, the amount of video data to be encoded/decoded grows exponentially. It is a long-standing challenge how to be able to encode/decode video data more efficiently, while maintaining the image quality of the decoded video data.

For example, the conventional intra prediction mode performs angular prediction on a current coded block by direct copy or interpolation by referring to reconstructed pixels from neighboring blocks. As a result, prediction samples using the conventional intra prediction mode have a limited degree of freedom in pixel value variation, particularly along the prediction direction. To further improve the coding efficiency, a matrix-based intra prediction (MBIP) mode is introduced by applying a linear matrix transform to reconstructed pixels in neighboring blocks to predict samples of a current coded block. However, current implementations of MBIP present new challenges to hardware/software implementations, such as requiring complex look-up table operations between codec blocks using different types of intra prediction methods and taking up a lot of space (especially on-chip) to store matrix coefficients.

Disclosure of Invention

Embodiments are described herein that relate to video data encoding and decoding, and more particularly, embodiments relate to systems and methods for video encoding and decoding using an improved matrix-based intra prediction (MBIP) codec mode.

According to a first aspect of the present application, a method of updating a most probable mode candidate list for a current block of video data is performed at an electronic device having one or more processing units and a memory storing a plurality of programs to be executed by the one or more processing units. The method comprises the following steps: identifying a neighboring block located at a predefined position relative to a current block and its associated matrix-based intra prediction mode; determining a conventional intra-prediction mode corresponding to the matrix-based intra-prediction modes for the neighboring blocks according to a predefined mathematical relationship between the conventional intra-prediction mode and the matrix-based intra-prediction mode; and conventional intra prediction modes associated with the neighboring blocks are inserted into the most probable mode candidate list according to a predefined order.

According to a second aspect of the present application, an electronic device includes one or more processing units, a memory, and a plurality of programs stored in the memory. The programs, when executed by one or more processing units, cause an electronic device to perform a method of updating a most probable mode candidate list for a current block of video data as described above.

According to a third aspect of the present application, a non-transitory computer readable storage medium stores a plurality of programs for execution by an electronic device having one or more processing units. The programs, when executed by one or more processing units, cause an electronic device to perform a method of updating a most probable mode candidate list for a current block of video data as described above.

According to a fourth aspect of the present application, a method of predicting a current block of video data using matrix-based intra prediction is performed at an electronic device having one or more processing units and a memory storing a plurality of programs to be executed by the one or more processing units. The method comprises the following steps: identifying one or more neighboring blocks relative to the current block; selecting a matrix-based intra prediction mode for predicting the current block among a plurality of matrix-based intra prediction modes; retrieving coefficients of a matrix and a bias vector corresponding to the selected matrix-based intra prediction mode from a storage device; and performing matrix-based intra prediction on the identified one or more neighboring blocks using the retrieved matrix and coefficients of the bias vector.

According to a fifth aspect of the present application, an electronic device includes one or more processing units, a memory, and a plurality of programs stored in the memory. The programs, when executed by one or more processing units, cause an electronic device to perform a method of predicting a current block of video data using matrix-based intra prediction as described above.

According to a third aspect of the present application, a non-transitory computer readable storage medium stores a plurality of programs for execution by an electronic device having one or more processing units. The programs, when executed by one or more processing units, cause an electronic device to perform a method of predicting a current block of video data using matrix-based intra prediction as described above.

Drawings

The accompanying drawings, which are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this specification, illustrate described embodiments and together with the description serve to explain the principles. Like reference numerals designate corresponding parts.

Fig. 1 is a block diagram illustrating an exemplary video encoding and decoding system according to some embodiments of the present disclosure.

Fig. 2 is a block diagram illustrating an exemplary video encoder according to some embodiments of the present disclosure.

Fig. 3 is a block diagram illustrating an exemplary video decoder according to some embodiments of the present disclosure.

Fig. 4A-4D are block diagrams illustrating how a frame is recursively quadtree partitioned into multiple video blocks of different sizes according to some embodiments of the disclosure.

Fig. 5A is a block diagram illustrating 67 candidate intra prediction modes for predicting a current coded block based on reconstructed neighboring blocks, according to some embodiments of the present disclosure.

Fig. 5B is a block diagram illustrating exemplary positions of five reconstructed neighboring blocks of a current codec block according to some embodiments of the present disclosure.

Fig. 6A and 6B are block diagrams illustrating two matrix-based intra prediction schemes of differently sized coded blocks according to some embodiments of the present disclosure.

Fig. 7 is a flow diagram illustrating an exemplary process by which a video codec implements a technique to generate a Most Probable Mode (MPM) candidate list, according to some embodiments of the present disclosure.

Detailed Description

Reference will now be made in detail to the present embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous non-limiting specific details are set forth in order to provide an understanding of the subject matter presented herein. It will be apparent, however, to one skilled in the art that various alternatives may be used without departing from the scope of the claims and that the subject matter may be practiced without these specific details. For example, it will be apparent to one of ordinary skill in the art that the subject matter presented herein may be implemented on many types of electronic devices having digital video capabilities.

Fig. 1 is a block diagram illustrating an example system 10 for encoding and decoding video blocks in parallel according to some embodiments of the present disclosure. As shown in fig. 1, system 10 includes a source device 12, source device 12 generating and encoding video data to be later decoded by a target device 14. Source device 12 and target device 14 may comprise any of a wide variety of electronic devices, including desktop or laptop computers, tablet computers, smart phones, set-top boxes, digital televisions, cameras, display devices, digital media players, video game machines, video streaming devices, and the like. In some embodiments, source device 12 and target device 14 are equipped with wireless communication capabilities.

In some embodiments, target device 14 may receive encoded video data to be decoded via link 16. Link 16 may include any type of communication medium or device capable of moving encoded video data from source device 12 to destination device 14. In one example, link 16 may include a communication medium that enables source device 12 to transmit encoded video data directly to target device 14 in real-time. The encoded video data may be modulated according to a communication standard, such as a wireless communication protocol, and transmitted to the target device 14. The communication medium may include any wireless or wired communication medium such as a Radio Frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network, such as a local area network, a wide area network, or a global network, such as the internet. The communication medium may include a router, switch, base station, or any other equipment that may facilitate communication from source device 12 to target device 14.

In some other embodiments, the encoded video data may be sent from the output interface 22 to the storage device 32. Subsequently, the encoded video data in storage device 32 may be accessed by target device 14 via input interface 28. Storage device 32 may include any of a variety of distributed or locally accessed data storage media such as a hard drive, blu-ray discs, DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing encoded video data. In another example, storage device 32 may correspond to a file server or another intermediate storage device that may hold encoded video data generated by source device 12. The target device 14 may access the stored video data from the storage device 32 via streaming or downloading. The file server may be any type of computer capable of storing encoded video data and transmitting the encoded video data to the target device 14. Exemplary file servers include web servers (e.g., for a website), FTP servers, Network Attached Storage (NAS) devices, or local disk drives. The target device 14 may access the encoded video data through any standard data connection suitable for accessing encoded video data stored on a file server, including a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., DSL, cable modem, etc.), or a combination of both wireless and wired connections. The transmission of the encoded video data from the storage device 32 may be a streaming transmission, a download transmission, or a combination of both.

As shown in fig. 1, source device 12 includes a video source 18, a video encoder 20, and an output interface 22. Video source 18 may include sources such as the following or a combination of such sources: a video capture device (e.g., a video camera), a video archive containing previously captured video, a video feed interface for receiving video from a video content provider, and/or a computer graphics system for generating computer graphics data as source video. As one example, if video source 18 is a video camera of a security monitoring system, source device 12 and destination device 14 may form a camera phone or video phone. However, embodiments described herein may be generally applicable to video codecs and may be applied to wireless applications and/or wired applications.

Captured, pre-captured, or computer-generated video may be encoded by video encoder 20. The encoded video data may be transmitted directly to the target device 14 via the output interface 22 of the source device 12. The encoded video data may also (or alternatively) be stored on storage device 32 for later access by target device 14 or other devices for decoding and/or playback. The output interface 22 may further include a modem and/or a transmitter.

The target device 14 includes an input interface 28, a video decoder 30, and a display device 34. Input interface 28 may include a receiver and/or a modem and receives encoded video data over link 16. The encoded video data transmitted over link 16 or provided on storage device 32 may include various semantic elements generated by video encoder 20 for use by video decoder 30 in decoding the video data. Such semantic elements may be included within encoded video data sent over a communication medium, stored on a storage medium, or stored on a file server.

In some embodiments, the target device 14 may include a display device 34, and the display device 34 may be an integrated display device and an external display device configured to communicate with the target device 14. Display device 34 displays the decoded video data to a user and may include any of a variety of display devices, such as a Liquid Crystal Display (LCD), a plasma display, an Organic Light Emitting Diode (OLED) display, or another type of display device.

Video encoder 20 and video decoder 30 may operate according to proprietary or industry standards such as VVC, HEVC, MPEG-4, Part 10, advanced video codec, AVC, or extensions of such standards. It should be understood that the present application is not limited to a particular video codec/decoding standard and is applicable to other video codec/decoding standards. It is generally recognized that video encoder 20 of source device 12 may be configured to encode video data according to any of these current or future standards. Similarly, it is also generally contemplated that video decoder 30 of target device 14 may be configured to decode video data in accordance with any of these current or future standards.

Video encoder 20 and video decoder 30 may each be implemented as any of a variety of suitable encoder circuitry, such as one or more microprocessors, Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), discrete logic, software, hardware, firmware, or any combinations thereof. When implemented in part in software, the electronic device may store instructions for the software in a suitable non-transitory computer-readable medium and execute the instructions in hardware using one or more processors to perform the video codec/decoding operations disclosed in this disclosure. Each of video encoder 20 and video decoder 30 may be included in one or more encoders or decoders, either of which may be integrated as part of a combined encoder/decoder (CODEC) in the respective device.

Fig. 2 is a block diagram illustrating an exemplary video encoder 20 according to some embodiments described in the present application. Video encoder 20 may perform intra-prediction coding and inter-prediction coding of video blocks within video frames. Intra-prediction coding relies on spatial prediction to reduce or remove spatial redundancy in video data within a given video frame or picture. Inter-prediction coding relies on temporal prediction to reduce or remove temporal redundancy in video data within adjacent video frames or pictures of a video sequence.

As shown in fig. 2, video encoder 20 includes a video data memory 40, a prediction processing unit 41, a Decoded Picture Buffer (DPB)64, an adder 50, a transform processing unit 52, a quantization unit 54, and an entropy encoding unit 56. Prediction processing unit 41 further includes a motion estimation unit 42, a motion compensation unit 44, a partition unit 45, an intra prediction processing unit 46, and an intra Block Copy (BC) unit 48. In some embodiments, video encoder 20 also includes an inverse quantization unit 58, an inverse transform processing unit 60, and an adder 62 for video block reconstruction. A deblocking filter (not shown) may be located between adder 62 and DPB 64 to filter block boundaries to remove blockiness from the reconstructed video. In addition to a deblocking filter, a loop filter (not shown) may be used to filter the output of adder 62. Video encoder 20 may take the form of fixed or programmable hardware units, or may be dispersed among one or more of the fixed or programmable hardware units shown.

Video data memory 40 may store video data to be encoded by components of video encoder 20. The video data in video data storage 40 may be obtained, for example, from video source 18. DPB 64 is a buffer that stores reference video data for use by video encoder 20 in encoding video data (e.g., in intra or inter prediction coding modes). Video data memory 40 and DPB 64 may be formed from any of a variety of memory devices. In various examples, video data memory 40 may be on-chip with other components of video encoder 20, or off-chip with respect to those components.

As shown in fig. 2, upon receiving the video data, a partition unit 45 within prediction processing unit 41 partitions the video data into video blocks. This partitioning may also include partitioning the video frame into slices, tiles (tiles), or other larger Codec Units (CUs) according to a predefined partitioning structure, such as a quadtree structure, associated with the video data. A video frame may be divided into multiple video blocks (or a set of video blocks called tiles). Prediction processing unit 41 may select one of a plurality of possible prediction coding modes, such as one of one or more inter-prediction coding modes of a plurality of intra-prediction coding modes, for the current video block based on the error results (e.g., coding rate and distortion level). Prediction processing unit 41 may provide the resulting intra-predicted or inter-predicted coded blocks to adder 50 to generate a residual block, and to adder 62 to reconstruct the coded block for subsequent use as part of a reference frame. The prediction processing unit 41 also supplies semantic elements such as motion vectors, intra mode indicators, partition information, and other such semantic information to the entropy encoding unit 56.

To select a suitable intra-prediction coding mode for the current video block, intra-prediction processing unit 46 within prediction processing unit 41 may perform intra-prediction coding of the current video block relative to one or more neighboring blocks in the same frame as the current block to be coded to provide spatial prediction. Motion estimation unit 42 and motion compensation unit 44 within prediction processing unit 41 perform inter-prediction coding of the current video block relative to one or more prediction blocks in one or more reference frames to provide temporal prediction. Video encoder 20 may perform multiple codec passes, for example, to select an appropriate codec mode for each block of video data.

In some implementations, motion estimation unit 42 determines the inter-prediction mode for the current video frame by generating motion vectors according to predetermined patterns within the sequence of video frames, the motion vectors indicating the displacement of Prediction Units (PUs) of video blocks within the current video frame relative to prediction blocks within the reference video frame. The motion estimation performed by motion estimation unit 42 is a process that generates motion vectors that estimate motion for video blocks. The motion vector may, for example, indicate the displacement of a PU of a video block within a current video frame or picture relative to a prediction block within a reference frame (or other codec unit), the prediction block being relative to a current block being codec within the current frame (or other codec unit). The predetermined pattern may designate video frames in the sequence as P-frames or B-frames. Intra BC unit 48 may determine vectors (e.g., block vectors) for intra BC coding in a similar manner as motion vectors determined by motion estimation unit 42 for inter prediction, or may determine block vectors using motion estimation unit 42.

In terms of pixel differences, which may be determined by Sum of Absolute Differences (SAD), Sum of Squared Differences (SSD), or other difference metrics, a prediction block is a block of the reference frame that is considered to closely match a PU of the video block to be coded. In some implementations, video encoder 20 may calculate values for sub-integer pixel positions of reference frames stored in DPB 64. For example, video encoder 20 may interpolate values for a quarter-pixel position, an eighth-pixel position, or other fractional-pixel positions of the reference frame. Accordingly, motion estimation unit 42 may perform a motion search with respect to the full pixel position and the fractional pixel position and output a motion vector with fractional pixel precision.

Motion estimation unit 42 calculates motion vectors for PUs of video blocks in inter-prediction coded frames by: the location of the PU is compared to locations of prediction blocks of reference frames selected from a first reference frame list (list 0) or a second reference frame list (list 1), each of which identifies one or more reference frames stored in the DPB 64. The motion estimation unit 42 sends the calculated motion vector to the motion compensation unit 44 and then to the entropy coding unit 56.

The motion compensation performed by motion compensation unit 44 may involve extracting or generating a prediction block based on the motion vector determined by motion estimation unit 42. Upon receiving the motion vector for the PU of the current video block, motion compensation unit 44 may locate the prediction block to which the motion vector points in one of the reference frame lists, retrieve the prediction block from DPB 64, and forward the prediction block to adder 50. Adder 50 then forms a residual video block of pixel difference values by subtracting the pixel values of the prediction block provided by motion compensation unit 44 from the pixel values of the current video block being coded. The pixel difference values forming the residual video block may comprise a luminance difference component or a chrominance difference component or both. Motion compensation unit 44 may also generate semantic elements associated with video blocks of the video frame for use by video decoder 30 in decoding the video blocks of the video frame. The semantic elements may include, for example, semantic elements defining motion vectors for identifying prediction blocks, any flag indicating a prediction mode, or any other semantic information described herein. Note that motion estimation unit 42 and motion compensation unit 44 may be highly integrated, but are illustrated separately for conceptual purposes.

In some embodiments, intra BC unit 48 may generate vectors and extract prediction blocks in a manner similar to that described above in connection with motion estimation unit 42 and motion compensation unit 44, but in the same frame as the current block being coded, and these vectors are referred to as block vectors rather than motion vectors. In particular, intra BC unit 48 may determine the intra prediction mode to be used to encode the current block. In some examples, intra BC unit 48 may encode current blocks using various intra prediction modes, e.g., during separate encoding passes, and test their performance through rate-distortion analysis. Next, intra BC unit 48 may select an appropriate intra prediction mode to use among the various tested intra prediction modes, and generate an intra mode indicator accordingly. For example, intra BC unit 48 may calculate rate-distortion values for various tested intra-prediction modes using rate-distortion analysis, and select the intra-prediction mode with the best rate-distortion characteristics among the tested modes for use as the appropriate intra-prediction mode. Rate-distortion analysis generally determines the amount of distortion (or error) between an encoded block and the original, unencoded block that was encoded to produce the encoded block, as well as the bit rate (i.e., number of bits) used to produce the encoded block. Intra BC unit 48 may calculate ratios from the distortion and rate for various encoded blocks to determine which intra prediction mode exhibits the best rate-distortion value for the block.

In other examples, intra BC unit 48 may use, in whole or in part, motion estimation unit 42 and motion compensation unit 44 to perform such functions for intra BC prediction according to embodiments described herein. In either case, for intra block copying, the prediction block may be a block that is considered to closely match the block to be coded in terms of pixel differences, which may be determined by Sum of Absolute Differences (SAD), Sum of Squared Differences (SSD), or other difference metrics, and the identification of the prediction block may include calculating values for sub-integer pixel locations.

Whether the prediction block is from the same frame according to intra prediction or from a different frame according to inter prediction, video encoder 20 may form a residual video block by subtracting pixel values of the prediction block from pixel values of the current video block being coded to form pixel difference values. The pixel difference values forming the residual video block may include both luminance component differences and chrominance component differences.

As an alternative to inter prediction performed by motion estimation unit 42 and motion compensation unit 44 or intra block copy prediction performed by intra BC unit 48 as described above, intra prediction processing unit 46 may intra predict the current video block. In particular, intra-prediction processing unit 46 may determine an intra-prediction mode for encoding the current block. To do so, intra-prediction processing unit 46 may, for example, encode the current block using various intra-prediction modes during separate encoding passes, and intra-prediction processing unit 46 (or a mode selection unit in some examples) may select an appropriate intra-prediction mode to use from the tested intra-prediction modes. Intra-prediction processing unit 46 may provide information to entropy encoding unit 56 indicating the intra-prediction mode selected for the block. Entropy encoding unit 56 may encode information indicating the selected intra-prediction mode in the bitstream.

After prediction processing unit 41 determines a prediction block for the current video block via inter prediction or intra prediction, adder 50 forms a residual video block by subtracting the prediction block from the current video block. The residual video data in the residual block may be included in one or more Transform Units (TUs) and provided to the transform processing unit 52. The transform processing unit 52 transforms the residual video data into residual transform coefficients using a transform such as Discrete Cosine Transform (DCT) or a conceptually similar transform.

Transform processing unit 52 may send the resulting transform coefficients to quantization unit 54. The quantization unit 54 quantizes the transform coefficients to further reduce the bit rate. The quantization process may also reduce the bit depth associated with some or all of the coefficients. The degree of quantization may be modified by adjusting a quantization parameter. In some examples, quantization unit 54 may then perform a scan of a matrix comprising quantized transform coefficients. Alternatively, entropy encoding unit 56 may perform scanning.

After quantization, entropy encoding unit 56 entropy encodes the quantized transform coefficients into a video bitstream using, for example, context-adaptive variable length coding (CAVLC), context-adaptive binary arithmetic coding (CABAC), semantic-based context-adaptive binary arithmetic coding (SBAC), Probability Interval Partition Entropy (PIPE) coding, or another entropy encoding method or technique. The encoded bitstream may then be transmitted to video decoder 30, or archived in storage device 32 for later transmission to video decoder 30 or retrieval by video decoder 30. Entropy encoding unit 56 may also entropy encode motion vectors and other semantic elements for the current video frame being coded.

Inverse quantization unit 58 and inverse transform processing unit 60 apply inverse quantization and inverse transform, respectively, to reconstruct the residual video block in the pixel domain for use in generating reference blocks for predicting other video blocks. As noted above, motion compensation unit 44 may generate motion compensated prediction blocks from one or more reference blocks of a frame stored in DPB 64. Motion compensation unit 44 may also apply one or more interpolation filters to the prediction blocks to calculate sub-integer pixel values for use in motion estimation.

Adder 62 adds the reconstructed residual block to the motion compensated prediction block produced by motion compensation unit 44 to produce a reference block for storage in DPB 64. The reference block may then be used by intra BC unit 48, motion estimation unit 42, and motion compensation unit 44 as a prediction block to inter-predict another video block in a subsequent video frame.

Fig. 3 is a block diagram illustrating an exemplary video decoder 30 according to some embodiments of the present application. The video decoder 30 includes a video data memory 79, an entropy decoding unit 80, a prediction processing unit 81, an inverse quantization unit 86, an inverse transform processing unit 88, an adder 90, and a DPB 92. Prediction processing unit 81 further includes a motion compensation unit 82, an intra prediction processing unit 84, and an intra BC unit 85. Video decoder 30 may perform a decoding process that is substantially reciprocal to the encoding process described above in connection with fig. 2 with respect to video encoder 20. For example, motion compensation unit 82 may generate prediction data based on motion vectors received from entropy decoding unit 80, and intra-prediction unit 84 may generate prediction data based on intra-prediction mode indicators received from entropy decoding unit 80.

In some examples, the units of video decoder 30 may be tasked to perform embodiments of the present application. Furthermore, in some examples, embodiments of the present disclosure may be dispersed in one or more of the plurality of units of video decoder 30. For example, intra BC unit 85 may perform embodiments of the present application alone or in combination with other units of video decoder 30, such as motion compensation unit 82, intra prediction processing unit 84, and entropy decoding unit 80. In some examples, video decoder 30 may not include intra BC unit 85, and the functions of intra BC unit 85 may be performed by other components of prediction processing unit 81 (such as motion compensation unit 82).

Video data memory 79 may store video data to be decoded by other components of video decoder 30, such as an encoded video bitstream. The video data stored in video data storage 79 may be obtained, for example, from storage device 32, from a local video source (such as a camera), via wired or wireless network communication of the video data, or by accessing a physical data storage medium (e.g., a flash drive or hard drive). Video data memory 79 may include a Coded Picture Buffer (CPB) that stores encoded video data from an encoded video bitstream. Decoded Picture Buffer (DPB)92 of video decoder 30 stores reference video data for use by video decoder 30 in decoding the video data (e.g., in intra or inter prediction coding mode). Video data memory 79 and DPB 92 may be formed from any of a variety of memory devices, such as Dynamic Random Access Memory (DRAM) (including synchronous DRAM (sdram)), magnetoresistive ram (mram), resistive ram (rram), or other types of memory devices. For illustrative purposes, video data memory 79 and DPB 92 are depicted in fig. 3 as two different components of video decoder 30. It will be apparent to those skilled in the art that video data memory 79 and DPB 92 may be provided by the same memory device or separate memory devices. In some examples, video data memory 79 may be on-chip with other components of video decoder 30, or off-chip with respect to those components.

During the decoding process, video decoder 30 receives an encoded video bitstream representing video blocks and associated semantic elements of an encoded video frame. Video decoder 30 may receive semantic elements at the video frame level and/or the video block level. Entropy decoding unit 80 of video decoder 30 entropy decodes the bitstream to generate quantized coefficients, motion vectors or intra prediction mode indicators, and other semantic elements. The entropy decoding unit 80 then forwards the motion vectors and other semantic elements to the prediction processing unit 81.

When a video frame is coded as an intra-prediction coded (I) frame or coded for an intra-coded prediction block in other types of frames, intra-prediction processing unit 84 of prediction processing unit 81 may generate prediction data for a video block of the current video frame based on the signaled intra-prediction mode and reference data from previously decoded blocks of the current frame.

When a video frame is coded as an inter-prediction coded (i.e., B or P) frame, the motion compensation unit 82 of the prediction processing unit 81 generates one or more prediction blocks for the video block of the current video frame based on the motion vectors and other semantic elements received from the entropy decoding unit 80. Each of the prediction blocks may be generated from a reference frame within one of the reference frame lists. Video decoder 30 may use a default construction technique to construct reference frame lists, list 0 and list 1, based on the reference frames stored in DPB 92.

In some examples, when encoding and decoding a video block according to the intra BC mode described herein, intra BC unit 85 of prediction processing unit 81 generates a prediction block for the current video block based on the block vector and other semantic elements received from entropy decoding unit 80. The prediction block may be within a reconstruction region of the same picture as the current video block defined by video encoder 20.

Motion compensation unit 82 and/or intra BC unit 85 determine prediction information for the video block of the current video frame by parsing the motion vectors and other semantic elements and then use the prediction information to generate a prediction block for the current video block being decoded. For example, motion compensation unit 82 uses some of the received semantic elements to determine a prediction mode (e.g., intra-prediction or inter-prediction) for coding a video block of the video frame, an inter-prediction frame type (e.g., B or P), construction information for one or more of the reference frame lists for the frame, a motion vector for each inter-prediction encoded video block of the frame, an inter-prediction state for each inter-prediction coded video block of the frame, and other information for decoding a video block in the current video frame.

Similarly, some of the received semantic elements, such as flags, may be used by intra BC unit 85 to determine that the current video block is predicted using an intra BC mode, build information for which video blocks of the frame are within the reconstruction region and should be stored in DPB 92, a block vector for each intra BC predicted video block of the frame, intra BC prediction status for each intra BC predicted video block of the frame, and other information for decoding the video blocks in the current video frame.

Motion compensation unit 82 may also perform interpolation using interpolation filters as used by video encoder 20 during encoding of video blocks to calculate interpolated values for sub-integer pixels of a reference block. In this case, motion compensation unit 82 may determine interpolation filters used by video encoder 20 from the received semantic elements and use these interpolation filters to generate prediction blocks.

Inverse quantization unit 86 inverse quantizes the quantized transform coefficients provided in the bitstream and entropy decoded by entropy decoding unit 80 using the same quantization parameter calculated by video encoder 20 for each video block in the video frame to determine the degree of quantization. Inverse transform processing unit 88 applies an inverse transform (e.g., an inverse DCT, an inverse integer transform, or a conceptually similar inverse transform process) to the transform coefficients in order to reconstruct the residual block in the pixel domain.

After motion compensation unit 82 or intra BC unit 85 generates a prediction block for the current video block based on the vector and other semantic elements, adder 90 reconstructs the decoded video block for the current video block by adding the residual block from inverse transform processing unit 88 to the corresponding prediction block generated by motion compensation unit 82 and intra BC unit 85. A loop filter (not shown) may be located between adder 90 and DPB 92 to further process the decoded video block. The decoded video blocks in a given frame are then stored in DPB 92, and DPB 92 stores reference frames for subsequent motion compensation of subsequent video blocks. DPB 92, or a memory device separate from DPB 92, may also store decoded video for later presentation on a display device, such as display device 34 of fig. 1.

In a typical video codec, a video sequence typically includes an ordered set of frames or pictures. Each frame may include three arrays of samples, denoted SL, SCb, and SCr. SL is a two-dimensional array of brightness samples. SCb is a two-dimensional array of Cb chroma samples. SCr is a two-dimensional array of Cr chroma samples. In other cases, the frame may be monochromatic and therefore include only one two-dimensional array of luminance samples.

As shown in fig. 4A, video encoder 20 (or more specifically segmentation unit 45) generates an encoded representation of a frame by first segmenting the frame into a set of Codec Tree Units (CTUs). A video frame may include an integer number of CTUs ordered consecutively in raster scan order from left to right and top to bottom. Each CTU is the largest logical codec unit and the width and height of the CTU is signaled by video encoder 20 in a sequence parameter set such that all CTUs in a video sequence have the same size of one of 128 × 128, 64 × 64, 32 × 32, and 16 × 16. It should be noted, however, that the present application is not necessarily limited to a particular size. As shown in fig. 4B, each CTU may include one coding and decoding tree block (CTB) of luma samples, two corresponding coding and decoding tree blocks of chroma samples, and semantic elements for coding and decoding samples of the coding and decoding tree blocks. The semantic elements describe the properties of different types of units of a coded block of pixels and how the video sequence may be reconstructed at video decoder 30, including inter or intra prediction, intra prediction modes, motion vectors, and other parameters. In a monochrome picture or a picture with three separate color planes, a CTU may comprise a single coding and decoding tree block and semantic elements for coding and decoding samples of the coding and decoding tree block. The coding and decoding tree blocks may be N × N sample blocks.

To achieve better performance, video encoder 20 may recursively perform tree partitioning, such as binary tree partitioning, quadtree partitioning, or a combination of both, on the codec tree blocks of the CTUs and partition the CTUs into smaller Codec Units (CUs). As depicted in fig. 4C, a 64 × 64 CTU 400 is first divided into four smaller CUs, each having a block size of 32 × 32. Of the four smaller CUs, CU 410 and CU 420 are each divided into four 16 × 16 CUs by block size. Both the 16 × 16 CU 430 and the CU 440 are further divided into four 8 × 8 CUs by block size. Fig. 4D depicts a quadtree data structure showing the final result of the segmentation process of the CTU 400 as depicted in fig. 4C, each leaf node of the quadtree corresponding to one CU of a respective size ranging from 32 x 32 to 8 x 8. Similar to the CTU depicted in fig. 4B, each CU may include a Codec Block (CB) of luma samples and two corresponding codec blocks of chroma samples of the same size frame, as well as semantic elements for coding the samples of the codec blocks. In a monochrome picture or a picture with three separate color planes, a CU may comprise a single codec block and semantic structures for coding and decoding samples of the codec block.

In some implementations, video encoder 20 may further partition the coded blocks of the CU into one or more mxn Prediction Blocks (PBs). A prediction block is a rectangular (square or non-square) block of samples to which the same prediction (inter prediction or intra prediction) is applied. A Prediction Unit (PU) of a CU may include a prediction block of luma samples, two corresponding prediction blocks of chroma samples, and semantic elements for predicting the prediction block. In a monochrome picture or a picture with three separate color planes, a PU may include a single prediction block and semantic structures used to predict the prediction block. Video encoder 20 may generate predicted luma, Cb, and Cr blocks for the luma, Cb, and Cr prediction blocks for each PU of the CU.

Video encoder 20 may generate the prediction block for the PU using intra prediction or inter prediction. If video encoder 20 uses intra-prediction to generate the prediction block for the PU, video encoder 20 may generate the prediction block for the PU based on decoded samples of the frame associated with the PU. If video encoder 20 uses inter-prediction to generate the prediction block for the PU, video encoder 20 may generate the prediction block for the PU based on decoded samples of one or more frames other than the frame associated with the PU.

After video encoder 20 generates the predicted luma block, the predicted Cb block, and the predicted Cr block for one or more PUs of the CU, video encoder 20 may generate the luma residual block for the CU by subtracting the predicted luma block of the CU from the original luma codec block of the CU such that each sample point in the luma residual block of the CU indicates a difference between a luma sample point in one of the predicted luma blocks of the CU and a corresponding sample point in the original luma codec block of the CU. Similarly, video encoder 20 may generate a Cb residual block and a Cr residual block for the CU, respectively, such that each sample in the Cb residual block of the CU indicates a difference between a Cb sample in one of the predicted Cb blocks of the CU and a corresponding sample in the original Cb codec block of the CU, and each sample in the Cr residual block of the CU may indicate a difference between a Cr sample in one of the predicted Cr blocks of the CU and a corresponding sample in the original Cr codec block of the CU.

Furthermore, as shown in fig. 4C, video encoder 20 may decompose the luma, Cb, and Cr residual blocks of the CU into one or more luma, Cb, and Cr transform blocks using quadtree partitioning. A transform block is a rectangular (square or non-square) block of samples to which the same transform is applied. A Transform Unit (TU) of a CU may include a transform block of luma samples, two corresponding transform blocks of chroma samples, and semantic elements for transforming the transform block samples. Thus, each TU of a CU may be associated with a luma transform block, a Cb transform block, and a Cr transform block. In some examples, the luma transform block associated with a TU may be a sub-block of a luma residual block of a CU. The Cb transform block may be a sub-block of a Cb residual block of the CU. The Cr transform block may be a sub-block of the Cr residual block of the CU. In a monochrome picture or a picture with three separate color planes, a TU may comprise a single transform block and semantic structures for transforming the samples of the transform block.

Video encoder 20 may apply one or more transforms to a luma transform block of a TU to generate a luma coefficient block for the TU. The coefficient block may be a two-dimensional array of transform coefficients. The transform coefficients may be scalars. Video encoder 20 may apply one or more transforms to Cb transform blocks of a TU to generate Cb coefficient blocks for the TU. Video encoder 20 may apply one or more transforms to a Cr transform block of a TU to generate a Cr coefficient block for the TU.

After generating the coefficient block (e.g., a luminance coefficient block, a Cb coefficient block, or a Cr coefficient block), video encoder 20 may quantize the coefficient block. Quantization generally refers to a process in which transform coefficients are quantized to potentially reduce the amount of data used to represent the transform coefficients, while providing further compression. After video encoder 20 quantizes the coefficient block, video encoder 20 may entropy encode semantic elements that indicate the quantized transform coefficients. For example, video encoder 20 may perform Context Adaptive Binary Arithmetic Coding (CABAC) on semantic elements that indicate quantized transform coefficients. Finally, video encoder 20 may output a bitstream that includes the bit sequence that forms a representation of the coded frames and associated data, the bitstream being stored in storage device 32 or transmitted to destination device 14.

Upon receiving the bitstream generated by video encoder 20, video decoder 30 may parse the bitstream to obtain semantic elements from the bitstream. Video decoder 30 may reconstruct frames of video data based at least in part on semantic elements obtained from the bitstream. The process of reconstructing the video data is substantially reciprocal to the encoding process performed by video encoder 20. For example, video decoder 30 may perform an inverse transform on coefficient blocks associated with TUs of the current CU to reconstruct residual blocks associated with the TUs of the current CU. Video decoder 30 also reconstructs the codec block of the current CU by adding samples of the prediction block for the PUs of the current CU to corresponding samples of the transform blocks of the TUs of the current CU. After reconstructing the coded blocks for each CU of a frame, video decoder 30 may reconstruct the frame.

As noted above, video codecs use mainly two modes, namely intra-frame prediction (or intra-frame prediction) and inter-frame prediction (or inter-frame prediction), to achieve video compression. It should be noted that IBC may be considered as intra prediction or third mode. Between the two modes, inter prediction contributes more to coding efficiency than intra prediction because a motion vector is used to predict the current video block from a reference video block.

Fig. 5A is a block diagram illustrating 67 conventional intra prediction modes for predicting a current coded block based on reconstructed neighboring blocks, according to some embodiments of the present disclosure. These 67 conventional intra prediction modes include 65 angular modes (shown as mode indices 2 through 33 being a "horizontal mode set" and mode indices 34 through 66 being a "vertical mode set") plus two non-angular modes, referred to as "planar mode" (mode index 0) and "DC mode" (mode index 1), collectively referred to as a "non-angular mode set". Embodiments of the present disclosure are applied to any number of angular modes for intra prediction. For example, the number of modes may be 35 as used in HEVC or some other number of modes greater than 35. Although embodiments may be applied to intra prediction mode coding of only a few selected color components, such as a luma component or a chroma component, it will be apparent to one of ordinary skill in the art that they may be applied to all available color components (luma and two chroma) or any other combination.

According to some embodiments of the present disclosure, a video codec, such as video encoder 20 or video decoder 30, may examine three or more neighboring blocks in a group of neighboring blocks to identify an intra-prediction mode, thereby generating a Most Probable Mode (MPM) candidate list for a current block. If a neighboring block is coded using an intra-prediction mode, the video codec may add the intra-prediction mode used to code the neighboring block to the MPM candidate list for the current block. The positions of the neighboring blocks checked by the video codec 20 may be fixed with respect to the current block.

Fig. 5B is a block diagram illustrating exemplary positions of five reconstructed neighboring blocks of a current codec block according to some embodiments of the present disclosure. For example, the positions of the five neighboring blocks may include a left (L) block, an above (a) block, a below-left (BL) block, an above-right (AR) block, and/or an above-left (AL) block. Other locations of adjacent blocks may also be used. The order in which the intra-prediction modes from the neighboring blocks are added to the MPM candidate list may depend on many factors, such as the current block size, whether the block has a certain shape (such as a rectangle or square), or based on context information (such as the size or shape of the neighboring blocks and the type or frequency of the intra-prediction modes of the neighboring blocks). Note that the five neighboring locations in fig. 5B are provided as an example, but fewer or more neighboring blocks may be considered when constructing the MPM candidate list using embodiments.

In general, a video codec may generate an MPM candidate list from different MPM types. Different types include, but are not limited to, neighbor-based intra prediction modes, derived intra prediction modes, and default intra prediction modes. The neighbor-based intra prediction mode refers to an intra prediction mode used for a neighboring block. The default intra prediction mode refers to a constant intra prediction mode that does not change with neighboring blocks. The default intra prediction mode(s) may be one of planar mode, DC mode, horizontal mode, or vertical mode. The derived intra prediction mode refers to an intra prediction mode derived from a neighbor-based intra prediction mode or a default intra prediction mode. The derived intra prediction mode may not be the actual intra prediction mode of the neighboring block. It may be an intra-prediction mode derived from the actual intra-prediction modes of the neighboring blocks or derived in some other way. For example, the derived intra prediction mode may be a neighbor-based intra prediction mode ± 1, ± 2, etc. The derived intra prediction mode may also be generated by another existing derived intra prediction mode.

The video codec may add the intra-prediction mode to the MPM candidate list according to the intra-prediction mode type. For example, the video codec may first add neighbor-based intra-prediction modes, then add the derived intra-prediction modes when the number of neighbor-based intra-prediction modes is less than N, and then add the default intra-prediction modes when the total number of neighbor-based intra-prediction modes and derived intra-prediction modes is still less than N. In another embodiment, the video codec may add different types of intra-prediction modes in an interleaved manner. For example, the video codec may add one or more default intra-prediction modes after adding a certain number of neighbor-based intra-prediction modes to the list. Alternatively, the video codec may add two neighbor-based intra prediction modes, two default intra prediction modes, and then add more neighbor-based intra prediction modes.

Only unique neighbor-based intra prediction modes will be added to the MPM candidate list. For example, if one of the neighboring blocks has the same intra prediction mode that has been added to the MPM candidate list, such a mode is not added to the list again. The position of the neighboring block may be represented by a sub-block size (e.g., 4 × 4), meaning that it is the granularity at which intra prediction mode information is stored. In another example, the intra prediction mode information may be specified per pixel or for larger blocks (such as 8 × 8). If the chroma components are sub-sampled compared to the luma components (such as in a 4: 2: 0 color format), the chroma component sub-block locations may be smaller, e.g., 2 × 2, which may correspond to luma 4 × 4.

In some implementations, depending on the neighboring block size, multiple positions of the neighboring block depicted in fig. 5B may belong to the same CU. For example, if the neighboring block is 16 × 16 and the block currently being coded is 8 × 8, the upper left position and the left position may belong to the same 16 × 16 neighboring block, where the intra prediction mode information will be the same for those positions.

The number of neighboring locations M may be equal to the MPM candidate list size N, but may be smaller or larger. In one example, the number M may be less than N to allocate some space to include other types of intra-prediction modes (e.g., derived intra-prediction modes or default intra-prediction modes) into the MPM candidate list. The number of locations may depend on characteristics of the current block and/or neighboring blocks, such as block size, whether the block is square or rectangular, whether the rectangular block is a horizontally oriented rectangular block (width greater than height) or a vertically oriented rectangular block (width less than height), the ratio between height and width, and the ratio between the greater and lesser of height and width. The number of positions may also depend on the prediction modes (e.g., intra or inter) of the neighboring blocks.

When a block is coded using an intra-prediction mode, a video encoder (e.g., video encoder 20) may generate an MPM candidate list for the block. A video decoder (e.g., video decoder 30) may generate the same MPM candidate list as determined by the video encoder by implementing the same MPM candidate list generation process implemented by the video encoder. Since the video encoder and the video decoder generate the same MPM candidate list, the video encoder may signal the intra-prediction mode to the video decoder by signaling an index value corresponding to a particular candidate in the MPM candidate list. Unless explicitly stated to the contrary, the MPM candidate list generation implementations described herein may be performed by a video encoder or a video decoder.

In addition to the aforementioned conventional intra prediction modes, a plurality of MBIP modes have been proposed for performing intra prediction on a current block from neighboring blocks by applying a linear matrix transform to reconstructed pixels of the neighboring blocks. Fig. 6A and 6B are block diagrams illustrating two matrix-based intra prediction schemes of differently sized coded blocks according to an embodiment of the present disclosure.

First, reconstructed pixels from the above-neighboring block and the left-neighboring block are filtered and optionally downsampled. For example, for the 8 x 8 codec block depicted in fig. 6B, 8 pixels from the upper and left neighboring blocks, respectively, are downsampled by a factor of 2 to derive 4 downsampled pixels from each side. Likewise, for the 4 × 4 codec block depicted in fig. 6A, 2 pixels from the upper and left neighboring blocks, respectively, are downsampled by a factor of 2 to derive 2 downsampled pixels from each side.

Second, the down-sampled pixels are rearranged into a one-dimensional vector, matrix multiplication is performed on the one-dimensional vector with a predefined matrix, and then a bias offset vector is added. After matrix multiplication and offset shifting, the results are rearranged back into a two-dimensional array to form a matrix-transformed two-dimensional result. Depending on the current block size, the matrix-transformed two-dimensional result may be in the sub-sample domain. For example, if the matrix-transformed two-dimensional result has a size of 4 × 4, it is considered to be in the sub-sample domain if the current block size is 8 × 8 (see, e.g., fig. 6B), and it is not considered to be in the sub-sample domain if the current block size is 4 × 4 (see, e.g., fig. 6A).

Finally, for the scenario depicted in fig. 6B, the matrix-transformed two-dimensional result is upsampled/interpolated to form a prediction value for the current codec block. But for the scenario depicted in fig. 6A, the two-dimensional result of the matrix transformation already has a size of 4 × 4, and no upsampling/interpolation is needed to form the prediction value for the current codec block. It is noted that the examples provided in fig. 6A and 6B are illustrative embodiments.

Although MBIP overcomes some of the problems associated with conventional intra prediction modes, it still introduces some new challenges to the design and implementation of new codec standards. For example, 67 MBIP modes require 67 coefficient matrices and 67 offset vectors. Assuming that each matrix/vector coefficient is a 10-bit precision number, it will take almost 8 kbytes of memory space to store these values. This may increase the physical size and power usage of chip-based implementations of MBIP.

In some embodiments, instead of using 10-bit precision for each coefficient in the MBIP matrix and the bias offset vector, lower precision is used to save the memory space required to store these coefficients. For example, 9-bit or even 8-bit precision is used for each coefficient in the MBIP matrix and the offset vector to save at least 10% of memory space.

In some embodiments, different precisions may be used for the coefficients in the MBIP matrix and the bias offset vector, respectively, because the codec efficiency derived from MBIP is not as sensitive to the precision of the bias offset vector as it is to the precision of the MBIP matrix. For example, 10-bit precision may still be used for the coefficients in the MBIP matrix, while a lower precision (e.g., 9 bits or less) is used for biasing the coefficients in the offset vector. Furthermore, it is possible to skip the offset vector completely. In other words, if the quality of the reconstructed pixels is satisfactory, MBIP performs matrix multiplication only on the pixels of the neighboring blocks and skips the addition of the offset vector to save more memory space.

In still other embodiments, only the MBIP matrices and offset vectors corresponding to the smallest block size are stored in memory, while other MBIP matrices and offset vectors corresponding to larger block sizes are upsampled and/or interpolated from those of the smallest size. For example, only the matrix and offset vector defined for the 4 x 4 block are saved. When the MBIP mode is applied to an 8 × 8 or 16 × 16 block, the MBIP matrix and bias offset defined for the 4 × 4 block are upsampled and/or interpolated (e.g., bilinear interpolation) accordingly to the size defined for the 8 × 8 or 16 × 16 block and then used to predict the current block.

As noted above in connection with fig. 6A and 6B, filtering and downsampling operations are applied to reconstructed pixels from neighboring blocks, which requires additional logic and therefore physical space for codec implementation.

In some embodiments, a 3-tap intra smoothing filter is used during filtering and/or downsampling in the MBIP mode, the 3-tap intra smoothing filter being applied to reconstructed pixels of neighboring blocks in the conventional intra prediction mode. In still other embodiments, no filtering operation is performed on reconstructed pixels of neighboring blocks prior to downsampling. In other words, downsampling is directly performed on reconstructed pixels from neighboring blocks without any filtering operation performed in advance.

The codec efficiency of the intra mode depends not only on the number of angular codec modes but also on the range of reconstructed samples that can be accessed. In some embodiments, reconstructed pixels from an upper right (AR), upper left (AL) and lower left (BL) block are also used in the filtering and downsampling process in the MBIP mode for better codec efficiency. In addition, when the current block is coded using the MBIP mode, different numbers of reconstructed pixels from the neighboring blocks may be used from the upper neighboring block (a) and from the left neighboring block (L), respectively. For example, if the aspect ratio of the current block is non-square (e.g., a vertical rectangle), in MBIP mode, more neighboring reconstructed pixels may be used from the left neighboring block (L) along the longer side of the current block than the shorter side of the current block. In some cases, when the aspect ratio of the current block exceeds a certain threshold (e.g., 3 to 1), only reconstructed pixels from neighboring blocks along the longer side of the current block are used in MBIP mode, and reconstructed pixels from neighboring blocks along the shorter side of the current block are not used at all.

Matrix multiplication is a computationally expensive operation. There are certain situations where: because the revenue associated with MBIP is unreasonable when compared to the complexity associated with MBIP, MBIP mode is disabled, e.g.,

if the width of the current block is four times the height of the current block;

if the height of the current coded block is four times the width of the current block;

if the width or height of the current block is greater than 64; and

if the current block is a chroma block.

When this occurs, a current block conforming to one of the above-described cases may be predicted using a conventional intra prediction mode, and an MPM candidate list is generated for the current block accordingly as described above. If one of the five neighboring blocks of the current block depicted in fig. 5B is predicted using the MBIP mode, such MBIP mode needs to be converted into a corresponding conventional intra prediction mode in order to be considered for predicting the current block.

Fig. 7 is a flow diagram illustrating an exemplary process by which a video codec implements a technique to generate a Most Probable Mode (MPM) candidate list, according to some embodiments of the present disclosure. As described above, this video codec may be the video encoder 20 or the video decoder 30. For illustrative purposes, this disclosure will use video encoder 20 as an example below.

It is assumed accordingly that video encoder 20 will process a current block of video data to be encoded. After determining that the current block is to be predicted using a conventional intra-prediction mode (e.g., one of the 67 modes depicted in fig. 5A), video encoder 20 needs to generate an MPM candidate list for the current block by examining one or more of the five neighboring blocks depicted in fig. 5B. Video encoder 20 first identifies (710) neighboring blocks located at predefined positions relative to the current block and their associated matrix-based intra prediction modes. Assuming that the left-neighboring block L is identified, video encoder 20 determines that the left-neighboring block L is reconstructed according to one of the MBIP modes. However, since the MBIP mode has been disabled for the current block, video encoder 20 needs to determine what conventional intra prediction mode will be associated with the left-neighboring block L when generating the MPM candidate list.

In some implementations, video encoder 20 determines (730) a conventional intra-prediction mode corresponding to the MBIP mode for the left-neighboring block L according to a predefined mathematical relationship between the conventional intra-prediction mode and the matrix-based intra-prediction mode. For example, video encoder 20 may assign (730-1) the left-neighboring block L a constant value (e.g., planar mode 0) regardless of the actual MBIP mode used to predict the left-neighboring block L. In other words, when video encoder 20 considers neighboring blocks used to update the MPM candidate list for the current block, a constant value corresponding to one of the conventional intra prediction modes is used to represent the neighboring blocks.

In some embodiments, the MBIP modes are designed such that there are specific MBIP modes that target block content in favor of DC intra prediction mode, planar intra prediction mode, and/or directional intra prediction mode, respectively. For example, the MBIP mode (e.g., mode 0) is selected to target block content favorable for plane prediction, the MBIP mode (e.g., mode 1) is selected to target block content favorable for DC prediction; and multiple MBIP modes (with values greater than 1) are selected to target block content in favor of angle prediction with different directions. As a result, the mapping between the MBIP mode and the conventional intra prediction mode becomes direct.

For example, assume that the MBIP intra prediction Mode is defined as Mode_MBIPAnd the normal intra prediction Mode is defined as Mode_INTRA(according to VVC, which ranges from 0 to 66), when the total number of MBIP modes is also 67, there is a one-to-one mapping between the conventional intra prediction mode and the MBIP mode as follows:

mapping regular intra prediction mode to MBIP mode;

set Mode_MBIP＝Mode_INTRA

Mapping MBIP mode to regular intra prediction mode:

set Mode_INTRA＝Mode_MBIP

In other words, when the total number of the conventional intra prediction modes is the same as the total number of the matrix-based intra prediction modes and the predefined mathematical relationship between the conventional intra prediction modes and the matrix-based intra prediction modes is defined as the conventional intra prediction modes having the same value as that of the matrix-based intra prediction modes (730-3).

When the total number of MBIP modes is 35, the following mapping logic is used for mode conversion:

mapping regular intra prediction mode to MBIP mode:

if Mode_INTRAHaving a value less than 2, Mode is set_MBIP＝Mode_INTRA；

Else, set Mode_MBIP＝(Mode_INTRA–34)/2+18。

Mapping MBIP mode to regular intra prediction mode:

if Mode_MBIPHaving a value less than 2, Mode is set_INTRA＝Mode_MBIP；

Else, set Mode_INTRA＝(Mode_MBIP–18)x 2+34。

Similarly, when the total number of MBIP modes is 19, the following mapping logic is used for mode conversion.

Mapping regular intra prediction mode to MBIP mode:

if Mode_INTRAHaving a value less than 2, Mode is set_MBIP＝Mode_INTRA；

Else, set Mode_MBIP＝(Mode_INTRA–34)/4+10。

Mapping MBIP mode to regular intra prediction mode:

if Mode_MBIPHaving a value less than 2, Mode is set_INTRA＝Mode_MBIP；

Else, set Mode_INTRA＝(Mode_MBIP–10)x 4+34。

When the total number of MBIP modes is 11, the following mapping logic is used for mode conversion:

mapping regular intra prediction mode to MBIP mode:

if Mode_INTRAHaving a value less than 2, Mode is set_MBIP＝Mode_INTRA；

Else, set Mode_MBIP＝(Mode_INTRA–34)/8+6。

Mapping MBIP mode to regular intra prediction mode:

if Mode_MBIPHaving a value less than 2, Mode is set_INTRA＝Mode_MBIP；

Else, set Mode_INTRA＝(Mode_MBIP–6)x 8+34。

In other words, when the total number of conventional intra prediction modes is greater than the total number of matrix-based intra prediction modes and the predefined mathematical relationship between the conventional intra prediction modes and the matrix-based intra prediction modes is defined as two categories: (i) non-angular intra prediction mode (less than mode 2) and (ii) angular intra prediction mode (equal to or greater than mode 2) (730-5). It should be noted, however, that in all of these cases, when the MBIP mode is enabled along with the conventional intra prediction mode, there is no need to store any mapping table for MPM list generation.

After determining the conventional intra-prediction mode, video encoder 20 inserts (750) the conventional intra-prediction modes associated with the neighboring blocks into the most probable mode candidate list according to a predefined order as described above in connection with fig. 5B.

In some embodiments, position-dependent intra prediction combining (PDPC) is applied to predicted samples formed by conventional intra prediction to improve intra prediction coding efficiency. The coding gain of PDPC results from the improvement in the quality of the prediction values produced from the combination of intra-predicted samples and reconstructed pixels from neighboring blocks. The PDPC may be executed on top of the MBIP mode. In other words, the PDPC operation is performed on the prediction value of the current block formed by the MBIP. Of course, such operations increase the computational complexity of the encoding/decoding operations and should be used at selective locations where the gain outweighs the cost.

In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, corresponding to tangible media (such as data storage media), or communication media, including any medium that facilitates transfer of a computer program (e.g., according to a communication protocol) from one place to another. In this manner, the computer-readable medium may generally correspond to (1) a non-transitory tangible computer-readable storage medium or (2) a communication medium, such as a signal or carrier wave. A data storage medium may be any available medium that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementing the embodiments described herein. The computer program product may include a computer-readable medium.

The terminology used in the description of the embodiments herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the claims. As used in the description of the embodiments and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms "comprises" and/or "comprising … …," when used in this specification, specify the presence of stated features, elements, and/or components, but do not preclude the presence or addition of one or more other features, elements, components, and/or groups thereof.

It will also be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first electrode may be referred to as a second electrode, and similarly, a second electrode may be referred to as a first electrode, without departing from the scope of embodiments. The first electrode and the second electrode are both electrodes, but they are not the same electrode.

The description of the present application has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications, variations and alternative embodiments will become apparent to those of ordinary skill in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments and with the best mode of practicing the invention in accordance with the principles and with various modifications as are suited to the particular use contemplated. Therefore, it is to be understood that the scope of the claims is not to be limited to the specific examples of the embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims.

Claims

1. A method of updating a most probable mode candidate list for a current block of video data, the method comprising:

identifying a neighboring block located at a predefined position relative to a current block and its associated matrix-based intra prediction mode;

determining a regular intra-prediction mode corresponding to the matrix-based intra-prediction mode for the neighboring block according to a predefined mathematical relationship between regular intra-prediction modes and matrix-based intra-prediction modes; and is

Inserting the conventional intra-prediction modes associated with the neighboring blocks into the most probable mode candidate list according to a predefined order.

2. The method of claim 1, wherein the predefined mathematical relationship between the conventional intra-prediction mode and the matrix-based intra-prediction mode is defined as the conventional intra-prediction mode being a constant value for different matrix-based intra-prediction modes.

3. The method of claim 1, wherein the total number of regular intra-prediction modes is the same as the total number of matrix-based intra-prediction modes, and the predefined mathematical relationship between the regular intra-prediction modes and the matrix-based intra-prediction modes is defined as the regular intra-prediction modes having the same value as the value of the matrix-based intra-prediction modes.

4. The method of claim 1, wherein the total number of regular intra-prediction modes is greater than the total number of matrix-based intra-prediction modes, and the predefined mathematical relationship between the regular intra-prediction modes and the matrix-based intra-prediction modes is defined as:

when the value of the matrix-based intra prediction mode is less than 2, the conventional intra prediction mode has the same value as the value of the matrix-based intra prediction mode; and

when the value of the matrix-based intra prediction mode is equal to or greater than 2, the conventional intra prediction mode has a value that is a linear function of the value of the matrix-based intra prediction mode.

5. The method of claim 1, wherein each matrix-based intra prediction mode has an associated matrix and bias vector, coefficients of the matrix and the bias vector having a precision of less than 10 bits.

6. The method of claim 1, wherein each matrix-based intra prediction mode has an associated matrix and bias vector, coefficients of the matrix and coefficients of the bias vector having different precisions.

7. The method of claim 6, wherein coefficients of the matrix have a higher precision than coefficients of the bias vector.

8. The method of claim 1, wherein a matrix-based intra prediction mode associated with the neighboring block has an associated matrix that is smaller in size than the neighboring block such that coefficients of the matrix are to be upsampled before being used to reconstruct the neighboring block.

9. An electronic device, comprising:

one or more processing units;

a memory coupled to the one or more processing units; and

a plurality of programs stored in the memory, which when executed by the one or more processing units, cause the electronic device to perform the method of claims 1-8.

10. A non-transitory computer readable storage medium storing a plurality of programs for execution by an electronic device having one or more processing units, wherein the plurality of programs, when executed by the one or more processing units, cause the electronic device to perform the methods of claims 1-8.

11. A method of predicting a current block of video data using matrix-based intra prediction, the method comprising:

identifying one or more neighboring blocks relative to the current block;

selecting a matrix-based intra prediction mode for predicting the current block among a plurality of matrix-based intra prediction modes;

retrieving coefficients of a matrix and a bias vector corresponding to the selected matrix-based intra prediction mode from a storage device; and is

Performing matrix-based intra prediction on the identified one or more neighboring blocks using the retrieved matrix and coefficients of the bias vector.

12. The method of claim 11, wherein coefficients of the matrix and the bias vector have a precision of less than 10 bits.

13. The method of claim 11, wherein coefficients of the matrix and coefficients of the bias vector have different accuracies.

14. The method of claim 13, wherein coefficients of the matrix have a higher precision than coefficients of the bias vector.

15. The method of claim 11, wherein coefficients of the matrix and the bias vector are upsampled prior to performing matrix-based intra prediction on the identified one or more neighboring blocks.

16. The method of claim 11, wherein performing matrix-based intra prediction on the identified one or more neighboring blocks using the retrieved matrix and coefficients of the bias vector further comprises:

multiplying pixels in the identified one or more neighboring blocks with coefficients of the retrieved matrix; and is

The coefficient of the retrieved bias vector is added to the multiplication result to generate a prediction value of the current block.

17. The method of claim 11, wherein performing matrix-based intra prediction on the identified one or more neighboring blocks using the retrieved matrix and coefficients of the bias vector further comprises:

multiplying pixels in the identified one or more neighboring blocks with the retrieved coefficients of the matrix as a predictor of the current block without adding the retrieved coefficients of the bias vector to the predictor of the current block.

18. An electronic device, comprising:

one or more processing units;

a memory coupled to the one or more processing units; and

a plurality of programs stored in the memory, which when executed by the one or more processing units, cause the electronic device to perform the method of claims 11-17.

19. A non-transitory computer readable storage medium storing a plurality of programs for execution by an electronic device having one or more processing units, wherein the plurality of programs, when executed by the one or more processing units, cause the electronic device to perform the methods of claims 11-17.